Docs: Use 'go get -d' to download the source without installing.
Docs: Use 'go get -d' to download the source without installing.

The build instructions in README.md should use 'go get -d' instead
of plain 'go get' to obtain the source code. Otherwise it'll attempt
to build and install the program, which won't work since version.go
is missing.

Issue: #1

magnusbaeck/logstash-filter-verifier